It is known that shaped polyester articles, for example, polyethylene terephthalate filaments, fibers or films, exhibit an excellent tensile strength, dimensional stability, Young's modulus and resistance to fatigue and creep, and, therfore, useful as a reinforcing material, for example, car tires, conveyer belts, V-belts and hoses.
However, it is also known that the polyester articles inherently have a poor bonding property to rubber or other polymeric materials.
It is assumed that the poor bonding property is due to a poor contribution of hydrogen bonds in the ester linkages in the polyester molecules, on the bonding activity thereof. Therefore, when a polyester article is used as the reinforcing material for a rubber article or other polymeric article, the above-mentioned excellent physical properties of the polyester articles cannot be satisfactorily utilized for reinforcing the rubber article or other polymeric article. Accordingly, in order to utilize the polyester articles as the reinforcing material, it is required to significantly improve the bonding property of the polyester articles to rubber or other polymeric materials.
In order to attain this requirement, a number of approaches have been taken in an attempt to enhance the bonding activity of the polyester material. For example, it was attempted to improve the bonding property of the polyester material by treating the surface of the polyester material with a highly activating compound, for example, an epoxy compound or isocyanate compound. This attempt is disclosed in Japanese Patent Application Publication Nos. 42-11482 and 42-9044(1967). However, the results of the attempt was unsatisfactory. That is, the surface-treated product exhibited an unsatisfactory bonding property to rubber and other polymeric materials, especially, at an elevated temperature. Also, it was found that the improvement in the bonding property caused the resultant improved polyester material to have an excessively high stiffness, a poor processability in a shaping or molding process and a poor resistance to fatigue fracture.